1. Field of the Invention
This invention relates generally to fastener driving tools, and more particularly, to a new and improved fastener driving tool that utilizes an energy storing flywheel that is selectively engaged by a fastener driving member in order to drive the member into engagement with a fastener, such as a nail or a staple, for the purpose of driving the fastener into a workpiece.
2. Description of the Prior Art
Fastener driving tools have utilized an energy storing flywheel for the purpose of storing energy to drive a fastener into a workpiece. Examples of representative fastener driving tools of this type are disclosed in U.S. Pat. Nos. 4,121,745; 4,129,240; 4,189,080; 4,298,072; 4,323,127; 4,519,535; 4,544,090; 4,558,747 and 4,721,170. In addition, U.S. Pat. No. 4,928,868, the inventor and assignee of which are the same as in the case of the present invention, discloses a fastener driving tool wherein an energy storing flywheel cooperates with an idler wheel to selectively engage a ram for driving a fastener into a workpiece. These patents disclose an elastic cord and pulley arrangement to return the ram to its starting position. Such elastic cords, besides requiring a fairly complex supporting structure, require periodic replacement.
U.S. Pat. Nos. 4,042,036; 4,129,240; 4,161,272; 4,204,622 and 4,290,493 disclose other fastener driving tools having a return mechanism that includes a helical tension spring to return the ram to its starting position. In general, such an arrangement requires undesirable headroom for the contracted spring. In addition, tension springs, in accordance with Hooke's Law, exert linearly increasing resistance to the ram as it is driven during a driving stroke such that the force by which a fastener is driven into the workpiece may be negatively affected.
The rams or blades utilized by the tools disclosed in a number of prior art patents are relatively complex in that they require friction pads that are engaged by the flywheel to transmit energy to the ram (see for example, U.S. Pat. Nos. 4,042,036, 4,555,747 and 4,323,127 which show blades having friction pads that require assembly). Alternatively, some rams are formed with narrowed or thinned portions. When the narrowed portion is disposed adjacent the flywheel, the flywheel is not able to drive the ram thereby providing a way of disengaging the blade from the flywheel at the end of a drive stroke.